This invention relates to a method for the continuous multi-stroke cutting of slots in flat, plate-shaped workpieces, especially sheet metal, by means of a slotting tool comprising two tool sections that are positioned on opposite sides of the workpiece and each provided with two longitudinal cutting edges which extend in the direction of the slot and transverse cutting edges at their longitudinal ends.
The longitudinal cutting edges on one tool section are sloped in the direction of the slot along an incline relative to the workpiece whereby, in the course of the process, the tool sections are moved relative to each other in the transverse direction of the workpiece and the slotting tool and the workpiece are moved relative to each other in the forward direction and, in their relative movement, the tool sections as shown perform operations in the form of slotting motions and at least one cross-cut or clipping stroke or motion so that, by means of the tool sections, each slotting motion cuts a strip of material that leaves a stem i.e., a connection at the slot ends with the remainder of the workpiece. This stem is then severed in a cross-cutting stroke by the same tool sections, and a gate-slotting function produces an end gate at a distance from the edge of the workpiece. The gate-slotting stroke is followed, prior to the cross-cutting stroke, by at least one slotting stroke and, in the process of the gate-slotting function and the slotting stroke following it, the workpiece is slotted over a length that exceeds the slot length maximally attainable in the cross-cutting stroke while, between the relative motions of the tool sections, the workpiece and the slotting tool are moved relative to each other by at least one forward increment in the feed direction.
The invention further relates to a machine for the multi-stroke, continuous slotting of plate-shaped workpieces, especially sheet metal, employing a slotting tool and a feed system by means of which the slotting tool and the workpiece are moved relative to each other in the forward direction and under control by a feed control unit. The slotting tool comprises two tool sections that are positioned on opposite sides of the workpiece and each is provided with two longitudinal cutting edges which extend in the direction of the slot and feature at their longitudinal ends transverse cutting edges extending between them. The longitudinal cutting edges on one tool section are inclined in the direction of the slot relative to the workpiece, and, by means of a cam drive controlled by a motion control unit, the tool sections can be moved relative to each other in the transverse direction of the workpiece by motions in the form of slotting strokes and at least one cross-cut clipping stroke or motion so that, by means of the tool sections, each slotting stroke cuts a strip of material that leaves a stem, i.e., a connection, at the slot end with the remainder of the workpiece. This stem is then severed in the cross-cutting motion by the same tool sections, while a gate-slotting function can produce a gate at one end of the slot which is spaced a distance from the edge of the workpiece. This gate-slotting stroke is followed, prior to the cross-cutting stroke, by at least one more slotting motion and, in the process of the gate-slotting stroke and the slotting stroke following it, the workpiece can be slotted over a length that exceeds the slot length maximally attainable in the cross-cutting stroke while, between the strokes of the tool sections, the workpiece and the slotting tool can be moved relative to each other by at least one forward increment in the feed direction.
When slotting plate-shaped workpieces and especially sheet metal, a great deal of significance is often attributed to obtaining cuts free from tool marks. Such high-quality cuts are currently produced by means of a method and a machine of the type described in U.S. Reissue Pat. No. 34,602. In that prior art approach, the slotting tool employs tool sections consisting of, on the top side of the workpiece to be processed, an upper die or punch that can be moved in the transverse direction of the workpiece and, cooperating with it, a lower die or swage positioned underneath the workpiece, and the lower die remains immobile in the transverse direction of the workpiece. Longitudinal cutting edges of the upper die are arched upwardly relative to the plane of the workpiece in the direction of the slot. For cutting a gate within the surface of the workpiece, the upper die is moved downwardly into the lower die or swage over a stroke length so gauged that, viewed in the direction of the slot, the rearward transverse cutting edge of the upper die moves past the corresponding transverse cutting edge of the swage, thus punching out the transverse rear end of the slot to be produced.
Apart from that cross cut, the gating cut also defines the initial part of the longitudinal boundaries of the slot. In the gating cut, the forward transverse cutting edge of the upper die, as viewed in the direction of the slot, is offset in height relative to the rearward transverse cutting edge and remains above the workpiece. Thus, as the gate cut is made, a strip of material is punched out laterally while its forward end in the direction of the slot is connected to the remaining body of the workpiece. Slotting strokes following the gate-cutting function extend the length of the strip of material. Accordingly, as a function of the selected cutting depth of the upper die along the swage, the forward stem connecting the strip of material to the remaining body of the workpiece is not severed. The arched shape of the longitudinal cutting edges of the upper die causes the laterally cut strip of material to be deflected into the inside of the swage. Transversely punching out the forward end of the finished slot severs the remaining connection between the strip of material and the body of the workpiece. To that effect the upper die or punch in its final motion is moved downwardly into the lower die swage deep enough for its forward transverse cutting edge to move past the corresponding transverse cutting edge of the swage.
In the case of the prior art approach as shown in U.S. Pat. No. Re. 34,602, severing the strip of material prior to the final motion of the upper die, i.e. before the cross-cutting stroke that finishes the slot, would be possible only if one can accept a lesser quality of the cutting surface. This is because, after the cross-cut is made, a lengthening of the slot would make it necessary for the tool sections to make a movement starting from a transverse slot end without any lateral cut. Experience has shown that, in any such case, undesirable tool marks are produced on the longitudinal sides of the slot at the starting point of that movement. It follows that, with the aforementioned process and the aforementioned machine, high-quality cuts are attainable only if one single cross-cut or clipping stroke is made, and that as the final motion. But severing, i.e. clipping, the punched out strip of material only when the final stroke is made can negatively affect the functional reliability of the slotting process and of the slotting tool itself. As a result, continuous multi-stroke slotting produces lengths of strips of material that make it difficult to accommodate lengthwise punched strips of material in the slotting tool in a manner that would not impede continued slotting.
A different type of method and a different type of slotting device are disclosed in U.S. Pat. No. 5,400,682. In that prior art system, the tool sections of the slotting tool consist of a bottom die or swage and, cooperating with it, two upper dies or punches. One of the two upper dies punches longitudinal slots into the workpiece, leaving a strip of material connected with the remainder of the workpiece at the forward end of the slot. The sole purpose of the second upper die is to sever the connecting stem between the strip of material and the body of the workpiece. In one variation of the method and machine design described in U.S. Pat. No. 5,400,682, the strip of material is clipped at a distance from its connecting point to the body of the workpiece. While this prevents tool marks on the longitudinal cutting surfaces of the slot thus produced, it requires a slotting tool that is complex in its mechanical design and in terms of control, that being a slotting tool with two separate, independently operated dies. After the gating slot stroke, the die or punch as shown performing that function is lifted into a position above the workpiece. The die remains in that position both during the return movement of the workpiece following the gating cut and during the ensuing cross-cutting operation. In that prior art machine, the length of the return travel is therefore independent of the upper die that executes the slotting motions.
It is the objective of this invention to advance the state of the art in U.S. Pat. No. RE. 34,602 in a manner that enhances the functional reliability of the earlier method and the earlier machine design while ensuring cut surfaces of high quality.
Another object is to provide such a method and a computer controlled machine which perform reliably and rapidly to produce clean slots without moving of the workpiece.